Solar power inverters are used to convert the DC power delivered by one or more PV cells (or solar cells) into an AC output power. The AC power may be coupled to a load, fed to an energy storage such as a battery or the like or it may be fed to a power grid. One known type of solar power inverter may include a plurality of PV inputs and a DC-DC converter at each of the PV inputs. The resulting DC power is then fed to a DC-AC inverter that provides the AC output power.
Multiple PV cells may be re-connected in parallel or series and arranged to form a solar module. A number of modules then may be connected to form a string and multiple strings are arranged to form a PV array.
The power delivered by a PV cell may vary over time due for example to variations in operating conditions such as changes in sunlight intensity, angle of incidence of sunlight, ambient temperature and other factors. PV cells accordingly are usually operated at an operating point at which the current and voltage values result in a power output as high as possible. This so called maximum power point (MPP) is a function of different, mostly environmental variables including light intensity and temperature. Power inverters for PV systems therefore often include some form of maximum power point tracking (MPPT) as a mechanism of identifying and tracking the MPP and controlling the power inverter to exploit the maximum possible power capacity of each PV cell.
US 2015/0085542 A1 from Delta Electronics Inc. discloses a photovoltaic module and a corresponding micro inverter of a solar power system. Based on the output power of the photovoltaic module it is decided whether or not the micro inverter enters a power boosting mode wherein the micro inverter delivers its maximum output power that is higher than its rated output power.
U.S. Pat. No. 8,093,756 B2 from AMPT LLC discloses control of an AC power system for renewable electrical energy such as to enhance the system efficiency. The DC power delivered by for example photovoltaic modules is converted in a first stage by a plurality of DC-DC converters. In a second stage, the converted DC power is converted to an AC power by a DC-AC inverter. In one aspect the output of the DC-DC converters is controlled by the DC-AC inverter for example by means of a direct control input. In this way, the system may be controlled such that that the DC-AC inverter has a high efficiency thereby independently controlling the DC-DC converters to maintain MPPT (Maximum Power Point Tracking).
Document U.S. Pat. No. 8,242,634 B2 discloses a solar energy system allowing an individualised control and analysis for overall field power control. The solar energy system includes a plurality of power sources each feeding into a dedicated DC-DC converter. The DC output of the DC-DC converters are fed to a DC-AC inverter providing an AC output connectable for example to a power grid. Different aspects are discloses such as power management with switch disconnect control, sequenced start of a solar power system or programmable power functionality control.
Despite the known MPP tracking the prior art does not reach the desired level of efficiency and the measures to be taken are typically rather complicated.